# A study of friction

According to the first law of motion, if an object is translationally in equilibrium velocity is constantthe sum of all the forces acting on the object must be equal to zero. For a person sitting on a chair, it can thus be postulated that a normal force is present balancing the gravitational force that pulls the sitting person down. However, it should be noted that only some of the normal force can cancel the other forces to zero like in the case of a sitting person.

Friction at the atomic level Determining the forces required to move atoms past each other is a challenge in designing nanomachines. In scientists for the first time were able to move a single atom across a surface, and measure the forces required.

Using ultrahigh vacuum and nearly zero temperature 5 Ka modified atomic force microscope was used to drag a cobalt atom, and a carbon monoxide molecule, across surfaces of copper and platinum. Such reasoning aside, however, the approximation is fundamentally an empirical construct.

It is a rule of thumb describing the approximate outcome of an extremely complicated physical interaction. The strength of the approximation is its simplicity and versatility.

Though in general the relationship between normal force and frictional force is not exactly linear and so the frictional force is not entirely independent of the contact area of the surfacesthe Coulomb approximation is an adequate representation of friction for the analysis of many physical systems.

When the surfaces are conjoined, Coulomb friction becomes a very poor approximation for example, adhesive tape resists sliding even when there is no normal force, or a negative normal force.

In this case, the frictional force may depend strongly on the area of contact. Some drag racing tires are adhesive for this reason. However, despite the complexity of the fundamental physics behind friction, the relationships are accurate enough to be useful in many applications.

This contradicts everyday experience in which an increase in normal force leads to an increase in friction.

Even its most simple expression encapsulates the fundamental effects of sticking and sliding which are required in many applied cases, although specific algorithms have to be designed in order to efficiently numerically integrate mechanical systems with Coulomb friction and bilateral or unilateral contact.

The latter were originally discovered in by George G. A connection between dry friction and flutter instability in a simple mechanical system has been discovered, [60] watch the movie for more details.

Frictional instabilities can lead to the formation of new self-organized patterns or "secondary structures" at the sliding interface, such as in-situ formed tribofilms which are utilized for the reduction of friction and wear in so-called self-lubricating materials.

Viscosity Fluid friction occurs between fluid layers that are moving relative to each other. This internal resistance to flow is named viscosity.

## Tribology - Wikipedia

In everyday terms, the viscosity of a fluid is described as its "thickness". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity.

The less viscous the fluid, the greater its ease of deformation or movement. All real fluids except superfluids offer some resistance to shearing and therefore are viscous. For teaching and explanatory purposes it is helpful to use the concept of an inviscid fluid or an ideal fluid which offers no resistance to shearing and so is not viscous.

Lubricated friction Main article: Lubrication Lubricated friction is a case of fluid friction where a fluid separates two solid surfaces. Lubrication is a technique employed to reduce wear of one or both surfaces in close proximity moving relative to each another by interposing a substance called a lubricant between the surfaces.

## What is friction? (article) | Khan Academy

In most cases the applied load is carried by pressure generated within the fluid due to the frictional viscous resistance to motion of the lubricating fluid between the surfaces. Adequate lubrication allows smooth continuous operation of equipment, with only mild wear, and without excessive stresses or seizures at bearings.

When lubrication breaks down, metal or other components can rub destructively over each other, causing heat and possibly damage or failure. Skin friction Main article: Parasitic drag Skin friction arises from the interaction between the fluid and the skin of the body, and is directly related to the area of the surface of the body that is in contact with the fluid.

Skin friction follows the drag equation and rises with the square of the velocity. Skin friction is caused by viscous drag in the boundary layer around the object.

There are two ways to decrease skin friction: The second method is to decrease the length and cross-section of the moving object as much as is practicable.Pierre Duhem examined Leonardo׳s understanding of statics and his other studies of mechanics in great detail in the context of his scientific antecedents and successors, but made no reference to his studies of friction.

Learn friction with free interactive flashcards. Choose from different sets of friction flashcards on Quizlet. Friction is the force that opposes the motion of an object. Learn about the sources of friction, identify examples of friction and test your knowledge with quiz questions. Friction: A Simple Case Study As can be seen from the calculations that follow (and the graph) the function al form of the velocity decay in these 3 cases is very different.

On the next 3 pages the the friction with in a way that takes the units into account by b1= 1/τ. 1. Introduction. Friction welding (FW) is a solid-state joining technique, by which significant heat is generated on the faying surfaces of two components under a certain combination of pressure, time, speed and surface roughness of weld face.

Whenever there is a change in motion, force is the responsible party. This activity will teach students more about how force and motion are related.

Friction stir welding - Wikipedia